The invention relates to an optical protective screen for improved visibility intended to be disposed in the field of view of an optical apparatus or a human observer.
Fine particles in motion, e.g. streams of dust or dirt, can deposit on a protective mask, window, lens, or the like, leading to reduced visibility which is a safety hazard e.g. for a motorcyclist.
A known protective device comprises a plurality of superposed thin transparent films, disposed on, e.g., the visor or mask of a motorcycle helmet. As each successive film becomes soiled, the motorcyclist removes it, exposing the next film. The overall thickness of the initial aggregate is limited, so as to avoid distortion of the field of view. Consequently, the useful life of one aggregate is limited, because the number of films which can be used in one aggregate is limited. Moreover, the motorcyclist must divert his attention while manipulating the device to remove a soiled film; this itself risks accidents.
Another known device which is applied to the visor or mask of a motorcycle helmet comprises a reel or the like, of transparent film, which is unrolled in front of the visor. Once the film is entirely used, it is replaced by reloading the device in a manner similar to reloading film in a photographic camera. The manipulations needed to replace the film in this device are somewhat complex. Also, the user is obliged to carry a spare reel of film, which is inconvenient.